First, we propose studying the effect of timolol maleate, a b-adrenergic antagonist, on the blood flow of the optic disk and choroid in the cat. The optic disk flow will be measured with a microelectrode to monitor hydrogen gas clearance. The choroidal blood flow will be measured by monitoring the clearance of indocyanine green dye from the choroidal circulation through a vortex vein. Second, we propose studying the effects of chronically elevated systemic blood pressure on chemically sympathectomized eyes of rhesus monkeys. The blood pressures will be elevated by coarctation of the thoracic aorta and the effects monitored by fluorescein angiography. Third, we will measure the preretinal oxygen tensions in alloxan diabetic dogs. Microelectrode oxygen tension measurements will be obtained with high blood sugars and following the administration of insulin.